Active Member

Can anybody offer advice on taking .025 off the head to bump the compression up..........here's why I ask.

In stock form, the combustion chamber is not symetrical with the machined surface of the head. It looks like the gasket surface of the head was skewed when machined making the combustion chamber cocked in relation to the deck. Between the deck and combustion chamber on one side, there is a .045 step and on the other side the deck has crept into the cylinder diameter wih no step. This makes the squish on the stepped side huuuge while on the other side, the piston is coming against the flat of the deck on the head.

I would like to register off of the dome of the combustion chamber and turn the deck down until the step disappears and open the combustion chamber back up to the correct diameter of the cylinder. My concern is that I will have no idea how much I have taken off oveall. It is recommended that only about .025 be taken off to still run on 91 octane pump gas.

H-M Supporter - Gold Member

I'm a newbie to machining, but have been an engine builder for all of my life. The way I would approach something like this is to try to determine if once you have the head gasket surfaced as you want it. Then is there enough area in the combustion chamber to remove material to open the chamber to the desired cc measurement of the combustion chamber. The 0.025" to remove gives you some measure of the combustion chamber when this has been performed, so you need to know this first, and then work to get the value after you resolve the head gasket deck issue. It may be just that specific head is not the one to rework, and you need a different one?

My experience with heads that are cast, and then machined, as most are, that the combustion chambers are a little different anyway, and it takes measuring the chambers with fluid to then remove material to balance them out.

You would need a burette graduated in milliliter to measure the combustion chamber volume.

I realize this thread is old, and you may have moved on with a solution by now.